Electrolyte for aluminum cells.



F. W. PEEK, 1R. ELEGTROLYTE FOR ALUMINUM CELLS.

APPLICATION FILED FEB.5, 1909.

1,008,860; Patented Nov. 14, 1911.

Electrolyte containing a bo'rate and a taftrate.

Witnesses Inventor-z Hisflttor'negg.

UNITED STATES PATENT OFFICE.

FRANK W. PEEK, T3,, SCHENEGTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

ELECTROLYTE FOR .ALU'MIHUM CIEKGLS.v

' Specification of Letters Patent. Patented NOV, 14;, 1911.

Application flied February 5, 1909. Serial No. 476,268.

T 0 all whom it may concern:

Be it known that I, FRANK W. PEEK, Jr., a citizen of the United States, residing at Schenectady, county of Schenectady, State of New York, have invented certain new and useful Improvements in Electrolytes for Aluminum Cells, of which the following is a specification.

My invention relates to electrolytic cells of the aluminum type, and merely for purposes of illustration, I have shown diagrammatically, in the accompanying drawing, one of the many forms of electrolytic cells in which my invention may be embodied, and in which a vessel 1 is provided with a cover 2 on which electrodes 3 are mounted to project into the electrolyte 4. As is well lmown, cells of this type consist essentially of electrodes, at least one of which is aluminum, and a suitable electrolyte. When a cell of this kind is included in an electric circuit,'and the aluminum electrode is made the anode, a thin film is formed upon its surface, which checks the flow of current through the cell. When both the electrodes consist of aluminum and the cell is included in an alternatingcurrent circuit it acts as a condenser, the electrode films servingas dielectreses. If thevoltage impressed upon the cell exceeds a certain critical breakdown voltage the in sulating property of the film is broken down'and a free discharge of current takes place through the cell. The breakdown voltage of a film depends upon several factors, the most controlling of which isthe character of the electrolyte. Should the cell be open-circuited for some length of'time, the insulating property of the film is impaired, possibly because of the dissolving effect on the part of the electrolyte, and it requires-a further passage of current to restore its insulating property.

According to my invention, I employ as electrolyte in cells of this character a solution consisting of a mixture of borates and tartrates, to which I add in some instances a'certain amount of glycerin. The glycerin when added to a neutral solution of the above mixture of salts appears to react in some manner, as the solution becomes acid. According to a modification of my mvention, the solution 1s once more neutralized entirely, or in part, after the addition of the glycerin.

Solutions of borates", such, for example, as ammonium borate, exert but a slight dissolving efl'ect upon the film, and their prop erties in other respects render them desirable as electrolytes for this class of cells. When, however, an aluminum cell containmg a solution of aborate as electrolyte has been in continuous operation for some time a depositrforms 'upon the plate, which impairs its efliciency. This deposit may be the product of electrochemical action occurring on the cell when included in the circuit.

I have found, however, that a deposit is formed in some cases even when the cell is not included in a circuit by the freezing of the electrolyte, and it may be caused even by the cooling of the electrolyte to a point near the freezing temperature. It is especially marked near. the surface of the electrolyte, where it may be started by evaporation of the solvent. No matter how it is formed, the deposit exerts a harmful ac-.

tion on the aluminum plates when a current is passing through the cell during its normal operation as a rectifier, lightning arrester or condenser. I have discovered that the growth of this deposit can be suppressed for the'greater part by the addition of tartrates to the electrolyte, and even when a deposit is formed in an electrolyte containing tartrates its injurious eflect on the plates is not as marked. Furthermore, the addition of the tartrate also has the effect of improving the character of the film both in cutting down the leakage current, which ordinarily passes through the cell when in circuit, and also in raising the critical or breakdown voltage of the same. I have also found that the presence,of. a tartrate in the electrolyte reduces its resistance.

When making up my solution I can, for example, begin with a mixture of boric or tartaric acids and using, for example, six parts boric acid and one of tartaric acid, and then adding an alkali to neutralize the acids. For this purpose a solution of ammonium, potassium, or sodium hydroxid can be used. It will, of course, be understood that it is not absolutely necessary to attain the exact neutral point, as a slight excess of acid or alkali is not injurious. Instead of starting with the boric acid, which when neutralized forms the normal borate, I may use the tetraborate, which is more stable. According to my present opinion, there is probably respective of any the successive steps as by Letters Patent of the formed by interaction of the borates and tartrates a complex salt, which may be termed a borotartrate. As already indicated, I add to this electrolyte, in some cases, a small amount of glycerin, for example, about 10%. The addition of the glycerin will cause the mixture, which formerly was neutral, to react acid. It is not unlikely that this efi'ect is due to the oxidation on the part of the glycerin to form an organic acid. However, my invention'may be practiced irtheory, by carrying out described above.

According to a modification of my inven- 'tion, the electrolyte is again neutralized, or partly neutralized, after the addition'of the glycerin by adding, for example, a solution of ammonirrmflhydroxid. The neutralization .is accompanied by the generation of heat and the liberation of gases.

I do not'olaim broadly in my present application thei use of glycerin in an electrolyte with subsequent neutralization of the acid formed thereby, as I intend to claim the same in another application.

What I claim as new, and desire to secure United States, is,-

1. In an electrolytic cell, the combination of electrodes and an electrolyte, consisting essentially of a solution of a borate and a tartrate.

2. In an electrolytic cell of the aluminum type, the combination of electrodes and an electrolyte containing a mixture of salts, one of which is a tartrate and another is-a borate.

3. In an electrolytic cell, the combination of electrodes and an electrolyte, consisting of a solution of ammonium.

4. In an electrolytic cell, the combination borates and tartrates of of electrodes and an electrolyte, consisting of borates, tartrates and glycerln.

5. In an electrolytic cell, the combination of electrodes and an electrolyte, consisting of a neutral solution of borates, tartrates and glycerin.

6. In an electrolytic cell of the aluminium type, an electrolyte consisting essentially of a solution of a borate and a tartrate of analkali in the proportion of about six to one respectively.

In witness whereof, I have hereunto set my hand this 4th day of February, 1909.

FRANK W. PEEK, J R. Witnesses:

MARGARET E. WOOLLEY,

HELEN Onrom). 

